This invention relates generally to an apparatus for centering one object within another object and particularly to an apparatus for centering a shadow mask frame in a kinescope faceplate panel.
A color picture tube includes a color selection electrode, commonly called a shadow mask, which causes the electron beams to impact phosphors of the proper light emitting color. Shadow masks are fabricated from thin conductive metal and include a large plurality of apertures and, accordingly, are flimsy and easily deformed. The shadow mask, therefore, is welded to a sturdy frame which lends physical support to the mask. Apertured support springs are welded to the sides of the frame. The apertures in the springs engage studs, which are embedded in the sidewalls of the glass faceplate panel, to support the mask within the panel. The black matrix and phosphor lines of which the screen is composed are formed by coating the inside surface of the panel with slurries of phosphor materials and exposing the slurries to light through the shadow mask apertures. Typically the apertures are rectangular with the long side arranged parallel to the direction of the phosphor and matrix lines. The screen lines are formed by moving the mask in the direction of the screen lines as the light passes through the apertures. The springs support the mask and frame in the panel in the orientation which existed when the springs were welded onto the frame. Accordingly, it is essential that the shadow mask frame be centered and properly oriented with respect to the faceplate panel while the springs are welded to the frame. For these reasons, there is a need for an apparatus for accurately centering, orienting and holding a shadow mask frame within a kinescope faceplate panel while the support springs are welded to the frame. The present invention fulfills this need.